TPS23754 datasheet(17/41 Pages) TI

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UVLO_R

Detection

Classification

PDPowered

Idle

CL_ON

CL_H

CU_OFF

CU_H

Note:VariablenamesrefertoElectricalCharacteristic

Tableparameters

DD-VSS

UVLO_H

Mark

MSR

TPS23754

TPS23754-1

TPS23756

www.ti.com

SLVS885D – OCTOBER 2008 – REVISED DECEMBER 2009

Table 2. Comparison of Operational Limits

POWER LOOP

PSE

PSE STATIC

PD INPUT

STATIC PD INPUT VOLTAGE

RESISTANCE

OUTPUT POWER

OUTPUT VOLTAGE

POWER

STANDARD

POWER

≤

POWER >

(max)

(min)

(max)

12.95 W

IEEE 802.3-2008

Ω

15.4 W

44 V

12.95 W

37 V–57 V

N/A

802.3at (Type 1)

802.3at (Type 2)

12.5

Ω

36 W

50 V

25.5 W

37 V–57 V

42.5 V–57 V

The PSE can apply voltage either between the RX and TX pairs (pins 1 - 2 and 3 - 6 for 10baseT or 100baseT),

or between the two spare pairs (4 - 5 and 7 - 8). Power application to the same pin combinations in 1000baseT

systems is recognized in IEEE 802.3at. 1000baseT systems can handle data on all pairs, eliminating the spare

pair terminology. The PSE may only apply voltage to one set of pairs at a time. The PD uses input diode bridges

to accept power from any of the possible PSE configurations. The voltage drops associated with the input

bridges create a difference between the standard limits at the PI and the TPS23754 specifications.

A compliant type 2 PD has power management requirements not present with a type 1 PD. These requirements

include the following:

1. Must interpret type 2 hardware classification

2. Must present hardware class 4

3. Must implement DLL negotiation

4. Must behave like a type 1 PD during inrush and startup

5. Must not draw more than 13W for 80ms after PSE applies operating voltage (power-up)

6. Must not draw more than 13W if it has not received a type 2 hardware classification or received permission

through DLL

7. Must meet various operating and transient templates

8. Optionally monitor for the presence or absence of an adapter (assume high power).

As a result of these requirements, the PD must be able to dynamically control its loading, and monitor T2P for

changes. In cases where the design needs to know specifically if an adapter is plugged in and operational, the

adapter should be individually monitored, typically with an optocoupler.

Threshold Voltages

The TPS23754 has a number of internal comparators with hysteresis for stable switching between the various

states. Figure 22 relates the parameters in the Electrical Characteristics section to the PoE states. The mode

labeled idle between classification and operation implies that the DEN, CLS, and RTN pins are all high

impedance. The state labeled Mark, which is drawn in dashed lines, is part of the new type 2 hardware class

state machine.

Figure 22. Threshold Voltages

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